Believe it or not, this is a review of Ready Player One.
Let's talk about adaptations from one medium to another. Specifically, the most common adaptation, book to movie.
But first, a story. I used to go to Comic Con when I lived in San Diego, and I saw a lot of neat things, most of which I've long since forgotten. One thing I haven't forgotten is the Stardust panel, which I presume was 2006. Actually, I have forgotten most of it, but one thing in particular stuck with me. In the Q&A portion, someone asked if the ending of the movie was the same as the ending of the book. For those who don't know, the ending is not the same - not at all. Neil Gaiman was there, and he paused, and looked serious, and then said words that I wish I had a recording of. Wait, scratch that - there's totally a video of this on YouTube. It's not exactly how I remember it, but it's the right answer. Just watch this and then come back.
Books and movies are different things. Even good movie adaptations aren't the same thing as the book, Stardust being an excellent example. Sometimes, a movie adaptation only loosely resembles the book - Starship Troopers, for instance, used some names from the book but completely changed plot, tone, and theme. For the most part, though, even movie adaptations that I don't like very much made the specific changes they made in order to make a coherent movie out of something that is inherently not a movie. Or, specific parts of otherwise decent adaptations might diverge from the source material in order to make the movie flow. In The Two Towers, for instance, Jackson changed Faramir's character specifically to influence the tension arc of the movie. I, like many Faramir fans, intensely dislike that change, but I understand why it was done, and the movie overall is still good.
Sometimes, a filmmaker adds or changes things for no discernible reason. For instance, Jackson's meddling with The Hobbit, which I have complained about at length elsewhere.
And, at last, this is what I have to say about Ready Player One: this is a perfectly fine adaptation of the book. The end result is a fun movie which has no more flaws than the source material does (the source material has some egregious flaws, largely but not exclusively in regards to sexism). It does not contain all the elements of the book, because it is not a book. Significant plot elements were changed, either to make the story more movie-like or because they couldn't get the rights - hard to say which in some cases. The end result, though, has fundamentally the same characters, structure, and plot arc that the book does, allowing for condensing due to time pressure.
And just in case you somehow read this far and haven't already read the book: Ready Player One is a nerdy and kinda shallow semi-apocalyptic sci-fi action movie, or a really nerdy and kinda dark (but still shallow) semi-apocalyptic sci-fi book. Not both at the same time.